I am lost!
Thread Starter
Burning Brakes
Joined: Oct 2020
Posts: 866
Likes: 73
I am lost!
My 77 C3 i bleed manual, and the pedal is so soft car barely stops.MC fairly new calipers fairly new, rubber hoses replaced. All i did to create problem after having high hard pedal and rear caliper hard line having a wet spot on fitting tightened a half turn. I have bled only that rear caliper inside first and outside last. No air just fluid came out. The fluid is clear. Any suggestions?
1967 Pedal Car Champion
Joined: Mar 2020
Posts: 9,135
Likes: 4,244
From: US-PNW
I'd start over at step one, which is to bleed the master. Raise the rear of the car so the master is at a forward tilt to move any air bubbles to the rear of the cylinder where they can escape. Try that to see how the pedal feels before going to each caliper again.
Safety Car
Joined: May 2001
Posts: 4,757
Likes: 1,647
From: Fairfax Virginia
I sympathize with your situation as many of us have been there before!
Personally I have been using a Phoenix Reverse Bleeder for decades but I am very familiar with the older ways of bleeding the brakes. Pushing air UP and OUT makes more sense than pushing it out the bottom.
While bleeding the brakes I found that tapping on the caliper will help release any trapped air inside of it. I tap with a light mallet and I don't bang on the parts. The bubbles will come loose from the tapping both the four calipers and the brass junction blocks. I have removed a lot of air from the calipers after I rebuilt them myself.
How old are the rubber hoses that connect the chassis to the calipers? They have been know to swell up and even collapse when they start to get old. Personally I chose to use the SS Braided Hoses for this application and I have been very happy with the results. The D.O.T. suggest they have a 15-20 year lifespan and should be replaced regularly.
It is not as likely but you might look to be sure that none of the brake lines has been damaged, crushed or twisted. I have seen them get twisted by over-anxious people when working on their brake system.
I hope that you find the cause of the issue and get your brakes back where they need to be to stop your Corvette safely!
Chris
Personally I have been using a Phoenix Reverse Bleeder for decades but I am very familiar with the older ways of bleeding the brakes. Pushing air UP and OUT makes more sense than pushing it out the bottom.
While bleeding the brakes I found that tapping on the caliper will help release any trapped air inside of it. I tap with a light mallet and I don't bang on the parts. The bubbles will come loose from the tapping both the four calipers and the brass junction blocks. I have removed a lot of air from the calipers after I rebuilt them myself.
How old are the rubber hoses that connect the chassis to the calipers? They have been know to swell up and even collapse when they start to get old. Personally I chose to use the SS Braided Hoses for this application and I have been very happy with the results. The D.O.T. suggest they have a 15-20 year lifespan and should be replaced regularly.
It is not as likely but you might look to be sure that none of the brake lines has been damaged, crushed or twisted. I have seen them get twisted by over-anxious people when working on their brake system.
I hope that you find the cause of the issue and get your brakes back where they need to be to stop your Corvette safely!
Chris
Thread Starter
Burning Brakes
Joined: Oct 2020
Posts: 866
Likes: 73
Hoses have been replaced . I just saw in my oldest corvette repair book a proportion block but on my 77 i can not seem to locate it . The book says under the MC not there. Can you bleed brakes after topping off with fluid with cover off?
Burning Brakes
Joined: Jul 2019
Posts: 783
Likes: 226
From: Salt Lake City
To your last question , yes. I am not clear on what started you on this project, and what you have done. I have never had to raise the rear of the car to bleed. You can start at the master as suggested. This takes two people. One holds pedal down while the other loosens lines at master. Do one at a time. Once you are sure there is no air in master, discs will usually bleed themselves if you just leave the fitting open and let fluid run through. Nothing wrong with tapping, although I haven't had to do that. Once fluid is running clear and bubble free you should have good pedal. I have seen masters fail after messing with peripherals due to stirring up crud that has been forming there. Bad master feels mushy and pedal slowly falls away as you hold pressure on it.. Through all of this remember that dot 3 fluid will damage your paint, and messes easily wash away with water. Good luck. I will be looking for more info on how this all started.
Last edited by OldVetteguy84; Jun 19, 2025 at 01:03 PM.
Burning Brakes
Joined: Apr 2020
Posts: 789
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From: Western NY
Pat
1967 Pedal Car Champion
Joined: Mar 2020
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From: US-PNW
If you look at the angle of the master on a power brake car (not sure about manual) it tilts backwards – all '77s had power brakes as standard equipment. An air bubble will get trapped at the forward end of the piston's cylinder and no amount of bleeding will displace it. By raising the rear so the master is slightly tilted forward this air bubble will move to the reservoir port and exit.
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1967 Pedal Car Champion
Joined: Mar 2020
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From: US-PNW
NO! There I said it!
Remove the bails so the cover is free to come off and relieves any vacuum from bleeding, but leave it covering the reservoirs. When bleeding, a stream of fluid often spurts out of the reservoir ports and can land on your paint.
Remove the bails so the cover is free to come off and relieves any vacuum from bleeding, but leave it covering the reservoirs. When bleeding, a stream of fluid often spurts out of the reservoir ports and can land on your paint.
Melting Slicks
Joined: Sep 2016
Posts: 2,228
Likes: 982
From: Wauconda IL
brake proportioning valve (also called a distribution block) for 1974-1977 C3 Corvettes. This valve has a switch that is part of it.
Location:
- This part is located on the front, left side of the vehicle.
- Specifically, it's positioned between the master cylinder and the front and rear brake lines.
- While the part number 339780 includes a switch, it is not simply a standalone brake light switch. It is a more complex component that controls brake fluid pressure distribution.
Thread Starter
Burning Brakes
Joined: Oct 2020
Posts: 866
Likes: 73
No i have not tried gravity bleeding. I just spent 3 hours on two calipers. Left rear loaded with air bubbles Pumping three times pedal and hold fluid comes slow then stops. Banging on caliper with rubber mallet helped! The rear left is loaded with air . I can not proceed to passenger side until i disperse of all air. Some thing is sucking air ,thanks god it is cool in garage. Tomorrow might be different ! will keep people informed. Never had a problem as this .
Le Mans Master
Joined: Mar 2004
Posts: 7,493
Likes: 1,502
From: Little Rock AR
Do the inner screw first on each caliper or it will take longer.
If you do the outer screw first, it will pull tiny bubbles from the inner pocket of air as the fluid goes past the inner screw.
If you do the outer screw first, it will pull tiny bubbles from the inner pocket of air as the fluid goes past the inner screw.
Racer
Joined: Jan 2024
Posts: 280
Likes: 112
It won't gravity bleed because the proportional valve tripped. You most likely have a Brake light on the dash.
You are chasing your tail. Remove the master cylinder and bench bleed it. Then bleed all 4 calipers. Avoid pressing the brake pedal to bleed it. I use Motive bleeder.
You are chasing your tail. Remove the master cylinder and bench bleed it. Then bleed all 4 calipers. Avoid pressing the brake pedal to bleed it. I use Motive bleeder.
Burning Brakes
Joined: Jul 2019
Posts: 783
Likes: 226
From: Salt Lake City
I have been fixing cars for 60 plus, but C3 is fairly new to me. Tilt of master trapping air makes sense.
But air bubbles don’t come from nowhere. If you continue to get bubbles, you have air entering somewhere. There should be a corresponding leak.
If there is no air but pedal won’t firm up it is possible calipers were reversed. I have seen that twice on other cars. Not sure if possible on C3. That is why I asked you to clearly state how you got started and what you have done.
But air bubbles don’t come from nowhere. If you continue to get bubbles, you have air entering somewhere. There should be a corresponding leak.
If there is no air but pedal won’t firm up it is possible calipers were reversed. I have seen that twice on other cars. Not sure if possible on C3. That is why I asked you to clearly state how you got started and what you have done.
Melting Slicks
Joined: Sep 2016
Posts: 2,228
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From: Wauconda IL
Thread Starter
Burning Brakes
Joined: Oct 2020
Posts: 866
Likes: 73
it started with hard pedal and a rear fitting that i had to tightened another half a turn it was the solid brake line i replaced on left rear. then after trying to bleed caliper i found right rear caliper puddle. i rebuilt that caliper but it would not even gravity bleed. I just got it to gravity bleed today and waiting for clamp to use motive bleeder. I ordered a new MC for it was leaking also.
Instructor
Joined: May 2012
Posts: 119
Likes: 2
From: Kennebunk, ME
I agree with all the suggestions listed above. Additionally, I found on my 68 with manual brakes that I had to reset the proportioning valve and purchase the screw in lock that goes were the sensor for the light goes. I had the same issue you described. Once I reset and locked the proportioning valve, I used a kit to loop the brake line connection back to the reservoir to bleed it, i then used a vacuum bleeder to get fluid through each of the bleeders on each caliper and I then gravity bled each bleeder on each caliper for 10 to 15 minutes each. When I pulled the lock out of the valve, I finally got an acceptable pedal.